Alka Dwivedi

Prevalence of SHANK3 variants in patients with different subtypes of autism spectrum disorders

Autism spectrum disorders (ASDs) include three main conditions: autistic disorder (AD), pervasive developmental disorder, not otherwise specified (PDD-NOS), and Asperger syndrome. It has been shown that many genes associated with ASDs are involved in the neuroligin–neurexin interaction at the glutamate synapse: NLGN3, NLGN4, NRXN1, CNTNAP2, and SHANK3. We screened this last gene in two cohorts of ASD patients (133 patients from US and 88 from Italy). We found 5/221 (2.3%) cases with pathogenic alterations: a 106 kb deletion encompassing the SHANK3 gene, two frameshift mutations leading to premature stop codons, a missense mutation (p.Pro141Ala), and a splicing mutation (c.1820-4 G>A). Additionally, in 17 patients (7.7%) we detected a c.1304+48C>T transition affecting a methylated cytosine in a CpG island. This variant is reported as SNP rs76224556 and was found in both US and Italian controls, but it results significantly more frequent in our cases than in the control cohorts. The variant is also significantly more common among PDD-NOS cases than in AD cases. We also screened this gene in an independent replication cohort of 104 US patients with ASDs, in which we found a missense mutation (p.Ala1468Ser) in 1 patient (0.9%), and in 8 patients (7.7%) we detected the c.1304+48C>T transition. While SHANK3 variants are present in any ASD subtype, the SNP rs76224556 appears to be significantly associated with PDD-NOS cases. This represents the first evidence of a genotype–phenotype correlation in ASDs and highlights the importance of a detailed clinical-neuropsychiatric evaluation for the effective genetic screening of ASD patients.

Association between deletion size and important phenotypes expands the genomic region of interest in Phelan–McDermid syndrome (22q13 deletion syndrome)

Background The clinical features of Phelan–McDermid syndrome (also known as 22q13 deletion syndrome) are highly variable and include hypotonia, speech and other developmental delays, autistic traits and mildly dysmorphic features. Patient deletion sizes are also highly variable, prompting this genotype–phenotype association study. Methods Terminal deletion breakpoints were identified for 71 individuals in a patient cohort using a custom-designed high-resolution oligonucleotide array comparative genomic hybridisation platform with a resolution of 100 bp. Results Patient deletion sizes were highly variable, ranging from 0.22 to 9.22 Mb, and no common breakpoint was observed. SHANK3, the major candidate gene for the neurologic features of the syndrome, was deleted in all cases. Sixteen features (neonatal hypotonia, neonatal hyporeflexia, neonatal feeding problems, speech/language delay, delayed age at crawling, delayed age at walking, severity of developmental delay, male genital anomalies, dysplastic toenails, large or fleshy hands, macrocephaly, tall stature, facial asymmetry, full brow, atypical reflexes and dolichocephaly) were found to be significantly associated with larger deletion sizes, suggesting the role of additional genes or regulatory regions proximal to SHANK3. Individuals with autism spectrum disorders (ASDs) were found to have smaller deletion sizes (median deletion size of 3.39 Mb) than those without ASDs (median deletion size 6.03 Mb, p=0.0144). This may reflect the difficulty in diagnosing ASDs in individuals with severe developmental delay. Conclusions This genotype–phenotype analysis explains some of the phenotypic variability in the syndrome and identifies new genomic regions with a high likelihood for causing important developmental phenotypes such as speech delay.

22q13.2q13.32 genomic regions associated with severity of speech delay, developmental delay, and physical features in Phelan-McDermid syndrome

Purpose:Phelan–McDermid syndrome is a developmental disability syndrome with varying deletions of 22q13 and varying clinical severity. We tested the hypothesis that, in addition to loss of the telomeric gene SHANK3, specific genomic regions within 22q13 are associated with important clinical features.Methods:We used a customized oligo array comparative genomic hybridization of 22q12.3-terminus to obtain deletion breakpoints in a cohort of 70 patients with terminal 22q13 deletions. We used association and receiver operating characteristic statistical methods in a novel manner and also incorporated protein interaction networks to identify 22q13 genomic locations and genes associated with clinical features.Results:Specific genomic regions and candidate genes within 22q13.2q13.32 were associated with severity of speech/language delay, neonatal hypotonia, delayed age at walking, hair-pulling behaviors, male genital anomalies, dysplastic toenails, large/fleshy hands, macrocephaly, short and tall stature, facial asymmetry, and atypical reflexes. We also found regions suggestive of a negative association with autism spectrum disorders.Conclusion:This work advances the field of research beyond the observation of a correlation between deletion size and phenotype and identifies candidate 22q13 loci, and in some cases specific genes, associated with singular clinical features observed in Phelan–McDermid syndrome. Our statistical approach may be useful in genotype–phenotype analyses for other microdeletion or microduplication syndromes.Genet Med 2014:16(4):318–328.

17p13.3 microduplications are associated with split-hand/foot malformation and long-bone deficiency (SHFLD)

Split-hand/foot malformation with long-bone deficiency (SHFLD) is a relatively rare autosomal-dominant skeletal disorder, characterized by variable expressivity and incomplete penetrance. Although several chromosomal loci for SHFLD have been identified, the molecular basis and pathogenesis of most SHFLD cases are unknown. In this study we describe three unrelated kindreds, in which SHFLD segregated with distinct but overlapping duplications in 17p13.3, a region previously linked to SHFLD. In a large three-generation family, the disorder was found to segregate with a 254 kb microduplication; a second microduplication of 527 kb was identified in an affected female and her unaffected mother, and a 430 kb microduplication versus microtriplication was identified in three affected members of a multi-generational family. These findings, along with previously published data, suggest that one locus responsible for this form of SHFLD is located within a 173 kb overlapping critical region, and that the copy gains are incompletely penetrant.

The historical Coffin–Lowry syndrome family revisited: Identification of two novel mutations of RPS6KA3 in three male patients

Coffin–Lowry syndrome (CLS) is a rare X‐linked dominant disorder characterized by intellectual disability, craniofacial abnormalities, short stature, tapering fingers, hypotonia, and skeletal malformations. CLS is caused by mutations in the Ribosomal Protein S6 Kinase, 90 kDa, Polypeptide 3 (RPS6KA3) gene located at Xp22.12, which encodes Ribosomal S6 Kinase 2 (RSK2). Here we analyzed RPS6KA3 in three unrelated CLS patients including one from the historical Coffin–Lowry syndrome family and found two novel mutations. To date, over 140 mutations in RPS6KA3 have been reported. However, the etiology of the very first familial case, which was described in 1971 by Lowry with detailed phenotype and coined the term CLS, has remained unknown. More than 40 years after the report, we succeeded in identifying deposited fibroblast cells from one patient of this historic family and found a novel heterozygous 216 bp in‐frame deletion, encompassing exons 15 and 16 of RPS6KA3. Drop episodes in CLS patients were reported to be associated with truncating mutations deleting the C‐terminal kinase domain (KD), and only one missense mutation and one single basepair duplication involving the C‐terminal KD of RSK2 in the patients with drop episode have been reported thus far. Here we report the first in‐frame deletion in C‐terminal KD of RPS6KA3 in a CLS patient with drop episodes.

Microdeletions on 6p22.3 are associated with mesomelic dysplasia Savarirayan type

Introduction Mesomelic dysplasias are a group of skeletal disorders characterised by shortness of the middle limb segments (mesomelia). They are divided into 11 different categories. Among those without known molecular basis is mesomelic dysplasia Savarirayan type, characterised by severe shortness of the middle segment of the lower limb. Objective To identify the molecular cause of mesomelic dysplasia Savarirayan type. Methods and results We performed array comparative genomic hybridisation in three unrelated patients with mesomelic dysplasia Savarirayan type and identified 2 Mb overlapping de novo microdeletions on chromosome 6p22.3. The deletions encompass four known genes: MBOAT1, E2F3, CDKAL1 and SOX4. All patients showed mesomelia of the lower limbs with hypoplastic tibiae and fibulae. We identified a fourth patient with intellectual disability and an overlapping slightly larger do novo deletion also encompassing the flanking gene ID4. Given the fact that the fourth patient had no skeletal abnormalities and none of the genes in the deleted interval are known to be associated with abnormalities in skeletal development, other mutational mechanisms than loss of function of the deleted genes have to be considered. Analysis of the genomic region showed that the deletion removes two regulatory boundaries and brings several potential limb enhancers into close proximity of ID4. Thus, the deletion could result in the aberrant activation and misexpression of ID4 in the limb bud, thereby causing the mesomelic dysplasia. Conclusions Our data indicate that the distinct deletion 6p22.3 is associated with mesomelic dysplasia Savarirayan type featuring hypoplastic, triangular-shaped tibiae and abnormally shaped or hypoplastic fibulae.

Deletion of 16q24.1 supports a role for the ATP2C2 gene in specific language impairment.

A 10-year-old boy presented with a history of significant delay in language acquisition as well as receptive and expressive language impairment that persisted into elementary school. In school, he exhibited difficulty with reading comprehension, telling and understanding narratives, and making inferences. Other aspects of his neurodevelopment were normal, with no history of significant medical concerns. He did not have hearing impairment, oromotor dysfunction, or specific neurologic abnormalities. He did not meet testing criteria for autism. Chromosomal microarray analysis and quantitative polymerase chain reaction determined that he had a de novo 159-kilobase deletion of chromosome 16q24.1 that included the ATP2C2 gene. ATP2C2 is a known candidate gene for specific language impairment and is postulated to have neurobiological significance in memory-related circuits. Our patients language deficits were consistent with a global type of specific language impairment impacting language comprehension, formulation, semantics, syntax, and phonology attributed to his de novo chromosome deletion.

LIS1 duplication: expanding the phenotype.

Disruptions to LIS1 gene expression result in neuronal migration abnormalities. LIS1 heterozygosity is a significant cause of lissencephaly, while overexpression has recently been noted in cases of microcephaly, ventriculomegaly, and dysgenesis of the corpus callosum with normal cortical gyration. We report a partial LIS1 duplication in a child with microcephaly, neurodevelopmental delays, and profound white matter atrophy in the absence of overt lissencephaly. The duplicated genetic segment was contained entirely within the first intron of LIS1, a segment that often contains inducers of transcription. Normal gyral patterns with mild volume loss were observed at birth. Follow-up cranial imaging revealed further white matter loss, diminished sulcation, and ventriculomegaly, suggesting expanding hydrocephalus ex vacuo. The radiographic pattern has not been documented in the presence of a LIS1 gene abnormality, and suggests that altered expression of LIS1 has wider phenotypic manifestations than currently defined.

Severe Hunter Syndrome (Mucopolysaccharidosis II) Phenotype Secondary to Large Deletion in the X Chromosome Encompassing IDS, FMR1, and AFF2 (FMR2):

A 2-year-old boy with an initial diagnosis of Hunter syndrome (mucopolysaccharidosis II) had a more severe phenotype than expected, which warranted further evaluation. The patient had severe infantile global neurodevelopmental delays, macrocephaly with a prominent forehead, coarse facial features with clear corneas, chronic congestion with snoring, wide-spaced teeth, short thick neck, hepatomegaly, an inguinal hernia repaired, early clawhand deformities, and severe generalized hypotonia. X chromosome microarray revealed a large deletion encompassing the genes IDS, FMR1, and AFF2 (FMR2) confirming the diagnoses of both Hunter and fragile X syndromes. This case is also a reminder to clinicians that for optimum patient care, further diagnostic testing is warranted if there is concern that a patient’s phenotype is more severe or complex than would be expected for the initial neurogenetic diagnosis.

Acquired Microcephaly in Blepharophimosis-Ptosis-Epicanthus Inversus Syndrome Because of an Interstitial 3q22.3q23 Deletion

BACKGROUND Blepharophimosis-ptosis-epicanthus inversus syndrome is an autosomal dominant condition because of mutations or deletions of the FOXL2 gene. Microcephaly is not associated with FOXL2 mutations but has been reported in individuals with chromosome 3q deletions, which include the FOXL2 gene and other contiguous genes. The ATR gene has been reported as a candidate gene for microcephaly in individuals with contiguous deletion of chromosome 3q involving the FOXL2 gene. PATIENT We describe a girl with blepharophimosis-ptosis-epicanthus inversus syndrome along with acquired microcephaly and intellectual disability. RESULTS Our patient had a deletion of chromosome 3q22.2q23, which does not include the ATR gene but does include the PIK3CB gene as a candidate gene for microcephaly. CONCLUSION We propose that the PIK3CB gene included in our patients chromosome 3q deletion may be the gene responsible for microcephaly and other patients with blepharophimosis-ptosis-epicanthus inversus syndrome because of a chromosome 3q deletion.